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Scope and lifetime of variable

Scope of a variable

The scope of a vriable is the part of the program for which the declaration is in effect.

In Java, the scope of such a variable is from its declaration to the end of the method.

Lifetime of a variable

The lifetime of a variable is the time period in which the variable has valid memory.

In Java, the lifetime of a variable is the period of time beginning when the method is entered and ending when execution of the method terminates.

Types of Scope of a varibale:

  • Local scope:¬†“visible” within function or statement block from point of declaration until the end of the block.
  • Global scope:¬†visible everywhere unless “hidden”.
  • Class scope: “seen” by class members.
  • Namespace scope: visible within namespace block.
  • File scope: visible within current text file.

Type with lifetime of variable:

  • Static: A static variable is stored in the data segment of the “object file” of a program. Its lifetime is the entire duration of the program’s execution.
  • Automatic: An automatic variable has a lifetime that begins when program execution enters the function or statement block or compound and ends when execution leaves the block. Automatic variables are stored in a “function call stack”.
  • Dynamic: The lifetime of a dynamic object begins when memory is allocated for the object (e.g., by a call to malloc() or using new) and ends when memory is deallocated (e.g., by a call to free() or using delete). Dynamic objects are stored in “the heap”.
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